1) Field of the Invention
The invention relates to systems used for enhancing the solar energy received by a solar array and, more particularly, to such systems which maintain the solar array in its desired position of facing the sun throughout diurnal operation of the system using the electrical power generated by a solar panel.
2) Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Worldwide energy demands have been steadily increasing as more people in more countries use energy consuming technologies in their daily lives. Fossil fuel sources of energy have therefore been increasing in cost as a result of this increasing demand. However, many alternatives to non-renewable energy sources such as nuclear energy and wind power devices have not been able to meet this increasing demand with clean, safe and non-polluting methods of utilization.
In the current field of exploiting renewable energy sources, there is a great increase worldwide in the use of solar energy facilities that use photovoltaic cells. Photovoltaic cells used for converting sunlight into electrical energy are placed in arrays and used for a variety of purposes. They are used as utility interactive power systems, as power supplies for remote or unmanned sites, as cellular phone switch site power supplies and as housing complex power supplies. Such arrays are able to produce from several kilowatts to over a hundred kilowatts of energy and can be installed wherever there is a reasonably flat area with exposure to the sun for significant portions of the day.
Companies producing and designing solar panels are receiving considerable funding from government sources in order to produce more efficient and cheaper designs. It is thus expected that the use of solar panels will become more widespread in the near future as the funding yields the anticipated improvements in solar panel designs. Many of the new designs are expected to be in the chemistry and structural makeup of the photovoltaic cells which are the constituents of the solar panels.
The efficiency and output of solar panels have been increased by panel clustering into the smallest possible space by forming large surfaces at a single level. But, this solution hinders panel cooling, reducing their yield due to the temperature increase at a ratio of 0.5% per degree Centigrade. This clustering is further limited due to panel expansion since the support structures are rigid and occasionally surrounded by a frame enclosing them, generating stresses between panels due to nighttime and daytime temperature differences. Such designs also have the important shortcoming of inherent structural instability as a result of asymmetrical static loads which has limited their use. Consequently, other ways of improving the performance of the solar panels have been developed which focus on maximizing the sunlight received by the photovoltaic cells.
A general principal is that the power generated by a solar panel depends strongly on the angle between the direction of propagation of solar rays irradiating the panel and a normal to the surface of the panel. Various forms of solar trackers have been developed for use with arrays of panels of photovoltaic cells to optimize the orientation of the solar panels so that it is normal to the direction of propagation of the solar rays throughout the day thereby increasing the concentration of light energy on the panels.
One type of conventional tracker used for solar power panels and solar collectors to improve their efficiency mounts the collector on a north-south axis and rotates it from east to west to follow the sun's apparent movement from sunrise to sunset. Typically, such systems include a pair of photovoltaic cells mounted on the solar collector or panel one cell of which views the eastern quadrant (90 degrees) of the horizon (when the collector and the cell are positioned in a horizontal plane) and the other cell of which views the western quadrant of the horizon. A difference in outputs between the cells indicates an error point at the sun, and thus the outputs of the cells are used to correctly reposition the solar collector. However, such systems are error prone. The presence of clouds and especially a single bright cloud can draw a photocell away from pointing at the sun and cause a drive system to miss-position a collector.
Another type of solar tracker system has photovoltaic panels configured in rows supported on a torque tube that serves as an axis. A tracker drive system rotates or rocks the rows to keep the panels as orthogonally oriented (relative to the sun) as possible. Typically, the rows are arranged with their axes disposed in a north-south direction and the trackers gradually rotate the rows of panels throughout the day from an east-facing direction in the morning to a west-facing direction in the afternoon. Subsequently, the rows of panels are manually brought back to the east-facing orientation for the next day.
A solar collector arrangement of this type is disclosed in U.S. Pat. No. 6,058,930 to Shingleton. In the Shingleton system, a tracker is associated with at least one row of panels. A north-south oriented torsion tube defines a north-south axis and an array of flat rectangular solar are attached in a generally balanced fashion on opposite sides of the torsion tube. The system uses at least one pier, and the footing of the pier is supported in the earth. A pivot member is affixed to the pier above its footing and the torsion tube is journalled in this pivot member. This permits the array of solar panels to be rotated on the north-south axis to follow the motion of the sun relative to the earth. The Shingleton arrangement is designed to enable the system to tolerate the stresses and loads that are imposed on the components of pier mounted solar array systems. However, an important disadvantage of such arrangements is that since many such conventional pier mounted designs do not track the apparent movement of the sun solar energy collection is not optimum and the panels have to be made larger than otherwise would be deemed necessary in order to improve upon the solar energy received. This basic design thus requires that it be made large which imposes heavy loads on the components thereof rendering them more failure prone than smaller system designs.
The most efficient trackers, for absorbing maximum sunlight in a given day, have been multiple axis trackers, which rotate about more than one axis so as to follow both the azimuth variation (progression of the sun's bearing angle i.e., east to south to west), and the sun's change in elevation angle from the horizon. These types of trackers can provide annual energy output improvements of 30%. These types of trackers are particularly beneficial to concentrating solar collectors. In such concentrating solar collectors, the received solar radiation is converted into a concentrated radiation beam before it is directed to the solar cells, and such designs are very sensitive to the angle of incidence of the solar radiation. Of the two solar tracker axes, azimuth orientation and elevation (or tilt) orientation, the first is more important since it provides a substantially greater energy production gain. In addition, the azimuth tracking axis can furthermore be easily carried out since it is exclusively a time function and therefore uniform throughout the year. In contrast, the tilt axis varies according to both the elevation changes as the sun moves during the day and the seasonal changes due to the tilt of the earth's orbit and its tracking is therefore more complex. Consequently, most large trackers presently installed provide only single axis tracking, and conventional multi axis systems presently installed generally have an inordinate degree of complexity. Their complexity presents numerous potential malfunction problems and inaccuracies. Reversing motors and computer driven reversing mechanisms as utilized in some of these systems also add to the cost. Many such systems also utilize very sophisticated and high precision components that must be shielded from environmental elements to which exposed in order to provide a reasonable degree of longevity. The required shielding structures and subsystems add to the cost and also add to the weight of the system necessitating structural reinforcements or higher strength support structures along with higher power motors.
Due to the complexity and structural instability problems associated with conventional solar tracking systems in addition to their increased cost, solar panel installations are typically of the fixed position type. They are fixed in a position in which the panels are oriented toward the south, depending on whether the installations are located north or south of the equator. The angle of inclination depends on the latitude of the installation site. But for such solar panel installations that are fixed in position, the exploitation of the solar radiation received is not as high as it otherwise could be since the direction of the perpendicular to the solar panel coincides rarely if ever with the direction of the solar rays on an annual basis. Consequently, the annual energy output of such solar installations is much less than optimal.
What is therefore needed is a structurally simple yet accurate system for tracking the sun's apparent diurnal movement. What is also needed is such a system which is capable of maximizing the solar energy gathering efficiency of the system for which the tracking is provided.